update docs

docs/src/SUMMARY.md

@@ -10,4 +10,5 @@
 # Reference Guide
 
 - [Accounts](accounts.md)
+- [Commodities](commodities.md)
 - [Allocation Targets](allocation-targets.md)

docs/src/commodities.md

@@ -0,0 +1,63 @@
+# Commodities
+
+There are no restrictions on the type of **commodities** that can be
+used in **paisa**. Anything like gold, mutual fund, NPS, etc can be
+tracked as a commodity. Few example transactions can be found below.
+
+```go
+2019/02/18 NPS
+    Asset:Equity:NPS:SBI:E            15.9378 NPS_SBI_E @ 23.5289 INR
+;// account name                      units   commodity   purchase price
+;//                                           name        per unit
+    Checking
+
+2019/02/21 NPS
+    Asset:Equity:NPS:SBI:E            1557.2175 NPS_SBI_E @ 23.8406 INR
+    Checking
+
+2020/06/25 Gold
+    Asset:Gold                        40 GOLD @ 4650 INR
+    Checking
+```
+
+**paisa** comes with inbuilt support for fetching the latest price of some
+commodities like mutual fund. For others, it will try to use the
+latest purchase price specified in the journal. For example, when you
+enter the second NPS transaction on `2019/02/21`, the valuation of
+your existing holdings will be adjusted based on the new purchase
+price.
+
+## Mutual Fund
+
+To automatically track the latest value of your mutual fund holdings,
+you need to link the commodity and the fund scheme code.
+
+```yaml
+commodities:
+  - name: NIFTY      # commodity name
+    type: mutualfund # type (only mutualfund supported as of now)
+    code: 120716     # mutual fund scheme code
+  - name: NIFTY_JR
+    type: mutualfund
+    code: 120684
+```
+
+The example config above links two commodities with their respective
+mutual fund scheme code. The scheme code can be found using the
+*search* command.
+
+```shell
+❯ paisa search mutualfund
+INFO Using config file: /home/john/finance/paisa.yaml
+INFO Using cached results; pass '-u' to update the cache
+✔ ICICI Prudential Asset Management Company Limited
+✔ ICICI Prudential Nifty Next 50 Index Fund - Direct Plan -  Growth
+INFO Mutual Fund Scheme Code: 120684
+```
+
+## Updates
+
+**paisa** fetches the latest price of the commodities only when
+*update* command is used. Make sure to run `paisa update` command
+after you make any changes to your journal file or you want to fetch
+the latest value of the commodities.