Added brief usage to README.

README.md

@@ -22,6 +22,35 @@ Common options:
 
 - `--set-default-currency` — set currency that'll be used as a default;
 
+## Brief usage with examples
+
+### Put coins in
+
+```bash
+piggybank [-r | --reversed] COINS in FILE [of CURRENCY]
+piggybank -r 1 4 5 4 6 8 in example.pb of SRUB
+```
+
+### Take coins out
+
+```bash
+piggybank [-r | --reversed] COINS from FILE
+piggybank -r 5 4 6 from example.pb
+```
+
+### Show information on your piggy bank
+
+```bash
+piggybank show FILE [with t(ransactions)]
+piggybank show example.pb with t
+```
+
+### Set default currency
+
+```bash
+piggybank --set-default-currency USD
+```
+
 ## How to put coins in
 
 ```bash